Step 1: Choose & Mark Material: Cut to Square
Measure and cut squares; make a corner to corner 'X' to find the center on both sides.
Step 2: Round off Squares
Use a band saw to cut as close to circular as possible. Keep in mind that slightly over size is better than under.
Step 3: Set Up Lathe: First Piece
Smooth off the outside and face surfaces of your wheel. You want to get it uniform and flat, maintaining the desired dimensions you want for the rest of the pieces.
Note that I lifted the guard up only to take photos.
Step 4: Make your Template
The most important thing is that the template wraps around two faces of the form, so you have something you're measuring off of.
If you're having trouble picturing what your shape will look like, try making some different 'revolves' in Autodesk Inventor. You can then laser cut the profiles you like as templates to try.
Step 5: Mark Key Template Points on the Wheel
Once you have the first marks, turn on the lathe and touch them with your sharpie to make them more visible.